Polyaspartic acid crosslinked particles, water absorbent, and method for producing polyaspartic acid crosslinked particles

Abstract

The present invention provides polyaspartic acid crosslinked particles with good water retention and water absorption under pressure, and a water-absorbing material containing the same. [Solution] A method for producing polyaspartic acid crosslinked particles, comprising a washing step S2 in which a PAsp crosslinked material consisting of at least one selected from the group consisting of polyaspartic acid crosslinked materials and salts thereof is washed using a mixed solution of water and alcohol or water. Preferably, the washing step S2 includes a dehydration step S3 in which the washed PAsp crosslinked material is dehydrated.

Description

[Technical Field]

[0001] This invention relates to cross-linked polyaspartate particles, a water absorbent, and a method for producing cross-linked polyaspartate particles. [Background technology]

[0002] Superabsorbent polymers can absorb tens to thousands of times their own weight in water. Absorbents containing superabsorbent polymers are used in a wide range of fields, including sanitary napkins, disposable diapers, and medical supplies such as poultices. A typical example of a superabsorbent polymer is acrylic acid-based superabsorbent polymer. However, acrylic acid-based superabsorbent polymers are not biodegradable. Therefore, the disposal method after use of acrylic acid-based superabsorbent polymers is becoming a problem.

[0003] In recent years, the use of polyaspartic acid as a water-absorbent resin has been considered. For example, Patent Document 1 describes a polyaspartic acid crosslinked material that can be applied to water-absorbent resins. Patent Document 1 also describes a method for producing a polyaspartic acid crosslinked material, which includes a step of reacting polysuccinimide (PSI), lysine as compound (A), and a polyfunctional epoxy (B) to produce a polyaspartic acid crosslinked material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2024-519300 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, conventional water-absorbing resins containing cross-linked polyaspartic acid particles had insufficient water retention and water absorption under pressure. Therefore, there was a need to improve the water retention and water absorption under pressure of cross-linked polyaspartic acid particles.

[0006] The present invention has been made in view of the above problems, and aims to provide polyaspartic acid crosslinked particles with good water retention and water absorption under pressure, and a water absorbent material containing the same. Furthermore, the present invention aims to provide a method for producing polyaspartic acid crosslinked particles that have good water retention and water absorption under pressure. [Means for solving the problem]

[0007] To solve the above problems and realize polyaspartic acid crosslinked particles with good water retention and water absorption under pressure, the inventors focused on the components contained in the polyaspartic acid crosslinked particles and diligently investigated them as shown below. The polyaspartic acid crosslinked particles contain water-soluble components such as raw material compounds that remain without forming a crosslinked structure, by-products generated during the reaction that forms the crosslinked structure, and compounds used during the reaction that forms the crosslinked structure.

[0008] The inventors conducted extensive research and found that these water-soluble components adversely affect the water retention and water absorption under pressure of particles containing polyaspartic acid crosslinked material. Furthermore, these water-soluble components were not removed even when isolation operations such as recrystallization, reprecipitation, filtration, and concentration were performed, which are normally carried out when isolating polyaspartic acid crosslinks from the reaction solution that produced the polyaspartic acid crosslinks. It was found that they were present in particles containing polyaspartic acid crosslinks at a high concentration of about 25% by mass. This is presumed to be because, due to the good water retention properties of the polyaspartic acid crosslinks, even when isolation operations are performed, the water-soluble components that are retained together with water in a dissolved state by the crosslinked structure are not easily discharged from the polyaspartic acid crosslinks.

[0009] Therefore, the inventors diligently studied how to produce particles containing a polyaspartic acid crosslinked material with a low water-soluble component content. As a result, it has been found that a polyaspartic acid crosslinked product with a low water-soluble component content can be produced by performing a washing step of washing the polyaspartic acid crosslinked product with a mixed solution of water and alcohol or water.

[0010] Furthermore, the present inventors have confirmed that particles containing a polyaspartic acid crosslinked product with a low water-soluble component content produced by the above method have excellent water retention and water absorption under pressure, and have conceived of the present invention. The present invention provides the following means.

[0011] [1] A method for producing polyaspartic acid crosslinked product particles, comprising a washing step of washing at least one PAsp crosslinked product selected from the group consisting of a polyaspartic acid crosslinked product and its salt with a mixed solution of water and alcohol or water.

[0012] [2] The method for producing polyaspartic acid crosslinked product particles according to [1], wherein the washing step includes a dehydration step of dehydrating the washed PAsp crosslinked product. [3] The method for producing polyaspartic acid crosslinked product particles according to [1], wherein the washing step includes a step of immersing the PAsp crosslinked product in the mixed solution or water having a mass 10 times or more and 100 times or less the mass of the PAsp crosslinked product and stirring for 0.5 hours or more and 1 hour or less.

[0013] [4] The method for producing polyaspartic acid crosslinked product particles according to [1], wherein the washing step includes a step of immersing the PAsp crosslinked product in the mixed solution or water having a mass exceeding 100 times and 600 times or less the mass of the PAsp crosslinked product and stirring for more than 1 hour and 16 hours or less.

[0014] [5] The method for producing polyaspartic acid crosslinked product particles according to [1], including a silica particle mixing step of arranging a plurality of the silica particles on the surface of the PAsp crosslinked product by mixing the washed PAsp crosslinked product and silica particles. [6] The method for producing polyaspartic acid crosslinked particles according to [5], wherein in the step of mixing the silica particles, the silica particles are mixed in an amount of 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the PAsp crosslinked body that has been washed and dried.

[0015] [7] The method for producing polyaspartic acid crosslinked particles according to [1], including a crosslinking step of reacting poly(succinimide) (PSI), lysine, and a polyfunctional epoxy compound to produce the PAsp crosslinked body.

[0016] [8] Containing a PAsp crosslinked body composed of at least one selected from the group consisting of polyaspartic acid crosslinked bodies and salts thereof, The polyaspartic acid crosslinked particles, wherein the content of the water-soluble component contained in the PAsp crosslinked body is 22% by mass or less.

[0017] [9] The polyaspartic acid crosslinked particles according to [8], wherein the PAsp crosslinked body includes a structure in which polyaspartic acid is crosslinked by lysine and a polyfunctional epoxy compound.

[10] The polyaspartic acid crosslinked particles according to [8], including a plurality of silica particles disposed on the surface of the PAsp crosslinked body.

[0018]

[11] A water absorbent containing the polyaspartic acid crosslinked particles according to any one of [8] to

[10] . [Advantages of the Invention]

[0019] In the polyaspartic acid crosslinked particles of the present invention, the content of the water-soluble component contained in the PAsp crosslinked body is a specific value or less and is sufficiently small. Therefore, they have excellent water retention and water absorption under pressure. Since the water absorbent of the present invention contains the polyaspartic acid crosslinked particles of the present invention, it has excellent water retention and water absorption under pressure.

[0020] The present invention provides a method for producing polyaspartic acid crosslinked particles, which includes a washing step of washing a PAsp crosslinked material, consisting of at least one selected from the group consisting of polyaspartic acid crosslinked material and its salts, using a mixed solution of water and alcohol or water. Therefore, according to the present invention's method for producing polyaspartic acid crosslinked particles, it is possible to produce polyaspartic acid crosslinked particles with a low content of water-soluble components and excellent water retention and water absorption under pressure. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a flowchart illustrating an example of a method for producing the polyaspartic acid crosslinked particles of this embodiment. [Modes for carrying out the invention]

[0022] Hereinafter, the polyaspartic acid crosslinked particles, water absorbent, and method for producing the polyaspartic acid crosslinked particles according to this embodiment will be described in detail with reference to the drawings as appropriate. The scope of the present invention is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the invention. Furthermore, if multiple upper and lower limits are given for a particular parameter, any upper and lower limit can be combined from among these upper and lower limits to obtain a suitable numerical range.

[0023] <Polyaspartate cross-linked particles> The polyaspartic acid crosslinked particles according to this embodiment mainly consist of a PAsp crosslinked material, which is selected from the group consisting of polyaspartic acid crosslinked materials and salts thereof. The polyaspartic acid crosslinked particles may also contain a plurality of silica particles arranged on the surface of the PAsp crosslinked material.

[0024] (PAsp crosslinked product) The PAsp crosslinked polymer contained in the polyaspartic acid crosslinked polymer particles is a polymer in which one or more side chains of polyaspartic acid are crosslinked. That is, the PAsp crosslinked polymer contains a structural unit (a) (hereinafter sometimes referred to as "structural unit (a)") which includes a crosslinked structure. The PAsp crosslinked polymer may also contain a structural unit (b) (hereinafter sometimes referred to as "structural unit (b)") which includes an uncrosslinked aspartic acid side chain, along with structural unit (a). Furthermore, the PAsp crosslinked polymer may also contain structural unit (a), a structural unit which includes an uncrosslinked aspartic acid side chain as structural unit (b) and does not contain an amino group, and a structural unit (c) (hereinafter sometimes referred to as "structural unit (c)") in which an amino group is introduced into the asparagine side chain.

[0025] (Construction unit (a) including the cross-linking structure) A structural unit (a) including a cross-linking structure is represented by the following general formula (1).

[0026] [ka] [In formula (1), R represents a divalent linking group.]

[0027] The constituent unit (a) represented by formula (1) includes a crosslinked structure in which two aspartic acid side chains are crosslinked with a crosslinking agent. Examples of crosslinked structures included in constituent unit (a) include a structure in which two aspartic acid side chains are crosslinked with a crosslinking agent compound (A) and a polyfunctional epoxy compound (B). A preferred example of such a constituent unit (a) is the constituent unit represented by the following general formula (2).

[0028] [ka] [In formula (2), L 1 and L 2 These are each independently divalent linking groups. The carboxyl group in formula (2) may form a salt.

[0029] -NHCH2-L in equation (2) above1 -C(COOH)H- is a structure derived from the crosslinking agent compound (A). L in formula (2) 1 Examples of the divalent linking group represented by include a linear or branched alkylene group, a combination of a linear or branched alkylene group and an ether bond, a combination of a methylene group and an ester bond, and the like. L 1 The divalent linking group represented by is preferably a linear alkylene group. L 1 When is a linear alkylene group, the number of carbon atoms is preferably 1 to 10, more preferably 2 to 8, and even more preferably 2 to 5.

[0030] -CH2-C(COOH)H-CH2-L in the formula (2) 2 -CH2-C(COOH)H-CH2- is a structure derived from the polyfunctional epoxy compound (B). L in formula (2) 2 Examples of the divalent linking group represented by include a linear or branched alkylene group, a combination of a linear or branched alkylene group and an ether bond, a combination of a methylene group and an ester bond, and the like.

[0031] L 2 The divalent linking group represented by is preferably a polyalkyleneoxy group. L 2 When is a polyalkyleneoxy group, the number of carbon atoms is preferably 1 to 10, more preferably 2 to 8, and even more preferably 2 to 4. L 2 is more preferably a polyethyleneoxy group or a polypropyleneoxy group, and even more preferably a polyoxyethylene group.

[0032] The carboxy group in the structural unit represented by the formula (2) may form a salt. The salt formed by the carboxy group in the formula (2) is preferably an alkali metal salt, and more preferably a sodium salt or a potassium salt.

[0033] The structural unit represented by formula (2) preferably has a structure in which two aspartic acid side chains are crosslinked by a crosslinking agent compound (A) which is lysine and a polyfunctional epoxy compound (B). A more preferred example of the structural unit represented by formula (2) is the structural unit represented by the following formula (3), which is crosslinked with lysine, which is a crosslinking agent compound (A), and ethylene glycol diglycidyl ether, which is a polyfunctional epoxy compound (B).

[0034] [ka] [The carboxyl group in formula (3) may form a salt.]

[0035] The carboxyl group (-COOH) in the constituent unit represented by formula (3) may form a salt. The salt formed by the carboxyl group in formula (3) is preferably an alkali metal salt, and more preferably a sodium salt or a potassium salt.

[0036] (Constituent unit (b) including uncrosslinked aspartic acid side chains) The structural unit (b) containing an uncrosslinked aspartic acid side chain is preferably a structural unit that contains an uncrosslinked aspartic acid side chain and does not contain an amino group (-NH2). Such a structural unit (b) is represented by the following general formula (4).

[0037] [ka] [In formula (4), G represents a carboxyl group or a carboxylate group.]

[0038] In formula (4) above, if G is a carboxylate group, a salt with a cation may be formed. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; and alkaline earth metal salts such as calcium salts and magnesium salts. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0039] (A structural unit in which an amino group is introduced into the asparagine side chain (c)) Examples of constituent units (c) in which an amino group (-NH2) is introduced to the asparagine side chain include monomer units represented by the following general formula (5).

[0040] [ka] [In formula (5), R 2 R represents a divalent linking group. 3 This represents a monovalent value.

[0041] The constituent unit (c) is preferably a constituent unit in which a crosslinking agent compound (A) is introduced into the side chain. Examples of such a constituent unit (c) include the constituent unit represented by the following general formula (6).

[0042] [ka] [In formula (6), L represents a divalent linking group. G represents a carboxyl group or carboxylate group.]

[0043] In formula (6), the divalent linking group represented by L is the same as L in formula (2). 1 Similar to the divalent linking group represented by , examples include linear or branched alkylene groups, combinations of linear or branched alkylene groups and ether bonds, and combinations of methylene groups and ester bonds. The divalent linking group represented by L is preferably a linear alkylene group. When L is a linear alkylene group, the number of carbon atoms is preferably 1 to 10, more preferably 2 to 8, and even more preferably 2 to 5.

[0044] In formula (6) above, if G is a carboxylate group, a salt with a cation may be formed. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0045] The constituent unit (c) is preferably a constituent unit in which lysine is introduced into the aspartic acid side chain. That is, the constituent unit (c) is preferably a constituent unit represented by the following formula (7).

[0046] [ka]

[0047] The PAsp crosslinks contained in the polyaspartic acid crosslinked particles according to this embodiment preferably include a structure in which polyaspartic acid is crosslinked with lysine and a polyfunctional epoxy compound. That is, the PAsp crosslink is a constituent unit represented by formula (2), and L in formula (2) 1 It is preferable that the material contains a constituent unit (a) which is a linear alkylene group having 3 carbon atoms. This is because it results in polyaspartic acid crosslinked particles with even better water retention and water absorption under pressure.

[0048] The PAsp crosslinker contained in the polyaspartic acid crosslinked particles of this embodiment is particularly preferably a constituent unit (a) represented by formula (3), a constituent unit (b) represented by formula (4), and a constituent unit (c) represented by formula (6), wherein L in formula (6) is a linear alkylene group having 3 carbon atoms. This is because polyaspartic acid crosslinked particles containing such a PAsp crosslinker exhibit a more pronounced improvement in water retention and water absorption under pressure, due to the low content of water-soluble components.

[0049] The polyaspartic acid crosslinked particles according to this embodiment have a water-soluble component content of 24% by mass or less, preferably 23% by mass or less, and more preferably 22% by mass or less. When the water-soluble component content of the PAsp crosslinked material is 24% by mass or less, the adverse effects on water retention and water absorption under pressure caused by the water-soluble component contained in the polyaspartic acid crosslinked particles are reduced. Therefore, the polyaspartic acid crosslinked particles of this embodiment have excellent water retention and water absorption under pressure. The water-soluble component content is more preferably 20% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less, and the lower the amount, the better.

[0050] Examples of water-soluble components that may be included in the PAsp crosslinked material contained in the polyaspartic acid crosslinked material particles according to this embodiment, in an amount of 24% by mass or less, include raw material compounds that remain without forming a crosslinked structure when used in the production of the PAsp crosslinked material, by-products generated during the reaction that forms the crosslinked structure, and additives such as pH adjusters used during the reaction that forms the crosslinked structure.

[0051] For example, if the PAsp crosslink contained in the polyaspartic acid crosslinked particles includes a constituent unit (a) represented by formula (3), a constituent unit (b) represented by formula (4), and a constituent unit (c) represented by formula (6), where L in formula (6) is a linear alkylene group with 3 carbon atoms, then the water-soluble components contained in the PAsp crosslink may include one or more compounds selected in any proportion from the raw material compounds shown in formulas (1A) and (1B) below, by-products shown in formulas (13) and (14), by-products other than the compounds shown in formulas (13) and (14), and compounds derived from additives used in the manufacturing process of the polyaspartic acid crosslinked particles.

[0052] [ka]

[0053] The compound represented by formula (1A) is lysine. Lysine is used as a crosslinking agent compound (A) and is a raw material compound that remains in the manufacturing process without forming a crosslinked structure. The compound represented by formula (1B) is ethylene glycol diglycidyl ether. Ethylene glycol diglycidyl ether is used as a polyfunctional epoxy compound (B) and is a raw material compound that remains in the manufacturing process without forming a crosslinked structure.

[0054] The compound shown in formula (13) is a by-product produced when polysuccinimide (PSI) and lysine shown in formula (1A) react during the reaction that forms the cross-linked structure of PAsp crosslinks. The compound represented by formula (14) is a by-product produced when lysine represented by formula (1A) and ethylene glycol diglycidyl ether represented by formula (1B) react during the reaction that forms the cross-linked structure of the PAsp crosslink.

[0055] The polyaspartic acid crosslinked particles of this embodiment may include a plurality of silica particles arranged on the surface of the PAsp crosslinked material. When a plurality of silica particles are arranged on the surface of the PAsp crosslinked material, the polyaspartic acid crosslinked particles have even better water absorption under pressure, which is preferable.

[0056] As silica particles contained in the polyaspartic acid crosslinked particles, it is preferable to use hydrophilic fumed silica particles such as amorphous silica, as these particles have good water absorption properties. The silica particles contained in the polyaspartic acid crosslinked particles have a specific surface area of, for example, 160 m². 2 / g or more 250m 2 It is possible to use those that are less than / g, 170m 2 / g or more 230m 2 It is preferable to use silica particles with a specific surface area of ​​160 m² or less. The reason is that the specific surface area of ​​silica particles is 160 m². 2This is because a value of 250 m² or more results in polyaspartic acid crosslinked particles with better water absorption properties. Furthermore, the specific surface area of ​​the silica particles is 250 m². 2 A value of less than / g is preferable because it suppresses swelling of the PAsp crosslinked material and makes it easier to adsorb onto the surface of the PAsp crosslinked material.

[0057] The silica particle content in the polyaspartic acid crosslinked particles is preferably 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of PAsp crosslinked material. This is because polyaspartic acid crosslinked particles with a silica particle content within the above range exhibit a more pronounced improvement in water absorption under pressure, due to the low content of water-soluble components. The silica particle content is more preferably 0.3% by mass or more. Furthermore, the silica particle content is more preferably 0.5% by mass or less.

[0058] <Method for producing cross-linked polyaspartate particles> Figure 1 is a flowchart illustrating an example of a method for producing the polyaspartic acid crosslinked particles of this embodiment. In the method for producing polyaspartic acid crosslinked particles according to this embodiment, as shown in Figure 1, the crosslinking step S1, washing step S2, dewatering step S3, drying step S4, silica particle mixing step S5, and heat treatment step S6 are performed in this order.

[0059] (Crosslinking step S1) In the crosslinking step S1 of this embodiment, a PAsp crosslinked material is produced by reacting polysuccinimide (PSI) with a crosslinking agent compound (A) and a polyfunctional epoxy compound (B). The PAsp crosslinked material, which is the reaction product of polysuccinimide (PSI), the crosslinking agent compound (A), and the polyfunctional epoxy compound (B), can be produced by the method described in Patent Document 1.

[0060] [Polysuccinimide (PSI)] Polysuccinimide (PSI) can be produced using aspartic acid as a raw material by known methods. Specifically, for example, it can be produced by mixing aspartic acid and phosphoric acid and heating the mixture.

[0061] [Crosslinking agent compound (A)] The crosslinking agent compound (A) has a first functional group (a1) and a second functional group (a2). The first functional group (a1) is preferably an amino group (NH2-). More preferably, the amino group of the first functional group (a1) is an NH2-CH2- amino group. The second functional group (a2) is preferably an amino group (NH2-) or a phosphonooxy group ((OH)2P(=O)-O-), and more preferably an amino group. When the second functional group (a2) is an amino group (NH2-), the amino group of the second functional group (a2) is preferably an amino group in the structure represented by the following formula (8).

[0062] [ka] [In formula (8), G represents a carboxyl group or carboxylate group. * represents a bond.]

[0063] When G in the structure represented by formula (8) is a carboxylate group, it may form a salt with a cation. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0064] When both the first functional group (a1) and the second functional group (a2) are amino groups (NH2-), it is preferable that the amino group of the second functional group of the crosslinking agent compound (A) has lower reactivity with polysuccinimide (PSI) than the amino group of the first functional group. Examples of such crosslinking agent compounds (A) include diamines with different terminal structures containing each amino group, such as asymmetric diamines.

[0065] The crosslinking agent compound (A) is preferably a compound in which the first functional group (a1) is an NH2-CH2- amino group and the second functional group (a2) is an amino group in the structure represented by formula (8) above. An example of such a crosslinking agent compound (A) is the compound represented by the following formula (9).

[0066] [ka] [In formula (9), L represents a divalent linking group.]

[0067] In formula (9), the divalent linking group represented by L can be a linear or branched alkylene group, a combination of a linear or branched alkylene group and an ether bond, or a combination of a methylene group and an ester bond. The divalent linking group represented by L is preferably a linear alkylene group. When L is a linear alkylene group, the number of carbon atoms in L is preferably 1 to 10, more preferably 2 to 8, and even more preferably 2 to 5.

[0068] The carboxyl group of the compound represented by formula (9) may form a salt. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, the salt of the carboxyl group of the compound represented by formula (9) is preferably an alkali metal salt, and more preferably a sodium salt or a potassium salt.

[0069] The crosslinking agent compound (A) is preferably a compound represented by the following formula (10).

[0070] [ka] [In equation (10), n represents an integer between 1 and 10.]

[0071] In formula (10) above, n is an integer between 1 and 10, preferably between 2 and 8, and more preferably between 3 and 5. The carboxyl group of the compound represented by formula (10) may form a salt. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, the salt of the carboxyl group of the compound represented by formula (10) is preferably an alkali metal salt, and more preferably a sodium salt or a potassium salt.

[0072] When the crosslinking agent compound (A) has an amino group as its first functional group (a1) and a phosphonooxy group ((OH)2P(=O)-O-) as its second functional group (a2), it is preferable that the compound is represented by the following formula (11).

[0073] [ka] [In formula (11), L represents a divalent linking group.]

[0074] The divalent linking group represented by L in formula (11) can be a linear or branched alkylene group, a combination of a linear or branched alkylene group and an ether bond, or a combination of a methylene group and an ester bond, similar to the divalent linking group represented by L in formula (9). The divalent linking group represented by L in formula (11) is preferably a linear alkylene group. When L is a linear alkylene group, the number of carbon atoms in L is preferably 1 to 10, more preferably 2 to 8, and even more preferably 3 to 5.

[0075] The phosphonooxy group in the compound represented by formula (11) may form a salt. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, the phosphonooxy group in the compound represented by formula (11) is preferably an alkali metal salt, and more preferably a sodium salt or a potassium salt.

[0076] Specific examples of crosslinking agent compounds (A) include lysine, ornithine, arginine, and phosphorylethanolamine. If the crosslinking agent compound (A) is a compound containing an amino group, an acidic salt of the above-mentioned amino group-containing compound may be used as the crosslinking agent compound (A). Examples of acidic salts of amino group-containing compounds include hydrochlorides and sulfates. Specifically, examples of such crosslinking agent compounds (A) include hydrochlorides of lysine hydrochloride, ornithine hydrochloride, arginine hydrochloride, etc., and sulfates of lysine sulfate, ornithine sulfate, arginine sulfate, etc. Among these, it is preferable to use lysine hydrochloride as the crosslinking agent compound (A).

[0077] [Polyfunctional epoxy compound (B)] Polyfunctional epoxy compounds (B) are compounds containing two or more epoxy groups. Examples of polyfunctional epoxy compounds include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, butanediol diglycidyl ether, and other alkane polyols (e.g., 2-6 carbon atoms) or poly(alkylene glycols) (e.g., 2-6 carbon atoms) polyglycidyl ethers; sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, erythritol polyglycidyl ether, trimethylol ethane polyglycidyl ether. Examples include polyglycidyl ethers of alkane polyols (e.g., 2-6 carbon atoms) such as glycidyl ether and trimethylolpropane polyglycidyl ether, and poly(alkylene glycol) (e.g., 2-6 carbon atoms); diepoxyalkanes (e.g., 4-8 carbon atoms) such as 1,2,3,4-diepoxybutane, 1,2,4,5-diepoxypentane, 1,2,5,6-diepoxyhexane, 1,2,7,8-diepoxyoctane, and 1,4- and 1,3-divinylbenzene epoxide; and polyphenol polyglycidyl ethers (e.g., 6-15 carbon atoms) such as 4,4'-isopropylidene diphenol diglycidyl ether (bisphenol A diglycidyl ether) and hydroquinone diglycidyl ether.

[0078] The polyfunctional epoxy compound (B) is preferably a bifunctional epoxy compound. The bifunctional epoxy compound is preferably an alkylene glycol diglycidyl ether, and most preferably an ethylene glycol diglycidyl ether. Examples of commercially available polyfunctional epoxy compounds (B) include the Denacol® series (EX-810, EX-861, EX-313, EX-614B, EX-512, etc.) manufactured by Nagase ChemteX Corporation.

[0079] In the crosslinking step S1 of the manufacturing method of this embodiment, it is preferable to react polysuccinimide (PSI) with lysine hydrochloride as a crosslinking agent compound (A) and ethylene glycol diglycidyl ether as a polyfunctional epoxy compound (B) in water to produce a PAsp crosslinked body.

[0080] In the crosslinking step S1 of this embodiment, the order in which the polysuccinimide (PSI), the crosslinking agent compound (A), and the polyfunctional epoxy compound (B) are reacted is not particularly limited. As the crosslinking step S1, for example, any of the following methods (i) to (iii) can be used. From the viewpoint of easily controlling the structure of the target PAsp crosslinked product, it is preferable to use method (i) or method (ii) among methods (i) to (iii), and more preferable to use method (i).

[0081] Method (i): A manufacturing method comprising the steps of reacting polysuccinimide (PSI) with a crosslinking agent compound (A) to obtain a reaction product (P1) of polysuccinimide (PSI) and crosslinking agent compound (A), and reacting the reaction product (P1) with a polyfunctional epoxy compound (B). Method (ii): A manufacturing method comprising first mixing polysuccinimide (PSI) and crosslinking agent compound (A), and then adding a polyfunctional epoxy compound (B) at a constant rate while the polysuccinimide (PSI) and crosslinking agent compound (A) react. Method (iii): A manufacturing method in which polysuccinimide (PSI), a crosslinking agent compound (A), and a polyfunctional epoxy compound (B) are mixed and then reacted.

[0082] The method described below is preferable for the above method (i). In other words, in the step of obtaining the reactant (P1), it is preferable to dissolve the crosslinking agent compound (A) in water to prepare an aqueous solution of the crosslinking agent compound (A), and then mix polysuccinimide (PSI) with the aqueous solution of the crosslinking agent compound (A) to react the polysuccinimide (PSI) with the crosslinking agent compound (A).

[0083] The aqueous solution of the crosslinking agent compound (A) is preferably prepared using, for example, 5 to 50 parts by mass of water per 1 part by mass of the crosslinking agent compound (A), and more preferably 10 to 30 parts by mass of water. Furthermore, the amount of polysuccinimide (PSI) mixed into the aqueous solution of the crosslinking agent compound (A) is preferably such that the ratio of crosslinking agent compound (A) to 100 parts by mass is 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 1.5 to 10 parts by mass.

[0084] Furthermore, the solution obtained by mixing polysuccinimide with an aqueous solution of the crosslinking agent compound (A) is preferably prepared so that the pH of the solution is 8 to 13 using an inorganic base compound such as sodium hydroxide and / or an organic base compound such as an amine. It is more preferable to adjust the pH of the above solution to 9 to 12, and even more preferable to adjust it to 11 to 11.5.

[0085] Furthermore, when using the above method (i), in the step of reacting the reactant (P1) with the polyfunctional epoxy compound (B), the reactant (P1) may be a solid reactant (P1) isolated from the reaction solution obtained in the step of generating the reactant (P1). In this case, it is preferable to react the reactant (P1) with the polyfunctional epoxy compound (B) by mixing the polyfunctional epoxy compound (B) into an aqueous solution of reactant (P1) obtained by dissolving the isolated solid reactant (P1) in water.

[0086] In the step of reacting reactant (P1) with polyfunctional epoxy compound (B), reactant (P1) may be used without isolating it from the reaction solution obtained in the step of generating reactant (P1). In this case, reactant (P1) and polyfunctional epoxy compound (B) can be reacted by adding polyfunctional epoxy compound (B) to the reaction solution obtained in the step of generating reactant (P1).

[0087] Furthermore, in the step of reacting the reactant (P1) with the polyfunctional epoxy compound (B), the amount of polyfunctional epoxy compound (B) per 100 parts by mass of reactant (P1) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass. By setting the amount of polyfunctional epoxy compound (B) per 100 parts by mass of reactant (P1) within the above range, a PAsp crosslinked body consisting of a massive gel can be produced.

[0088] Furthermore, the reaction temperature for reacting the reactant (P1) with the polyfunctional epoxy compound (B) can be, for example, 30°C to 100°C. The reaction temperature is preferably 40°C to 80°C, and more preferably 50°C to 70°C. The reaction time for the above reaction can be, for example, 40 minutes to 600 minutes, and preferably 60 minutes to 300 minutes, when the reaction temperature is 60°C.

[0089] (Cleaning process S2) In the washing step S2, the PAsp crosslinked material produced in the crosslinking step S1 is washed using a mixed solution of water and alcohol or water. In the washing step S2, if the PAsp crosslinked material generated in the crosslinking step S1 is a lumpy gel, it is preferable to perform a cutting step as a pretreatment step to cut the PAsp crosslinked material into string-like or granular shapes. The method for cutting the PAsp crosslinked material is not particularly limited and can be any known cutting device.

[0090] In the pretreatment process, after the cutting process, if necessary, a drying and grinding process may be performed to dry and grind the string-like or granular PAsp crosslinked material obtained by cutting into particles. In the drying and grinding process, it is preferable to grind the material so that the particle size measured using a sieve is 1000 μm or less, and more preferably so that the particle size is 750 μm or less.

[0091] In the drying and grinding process, for example, it is preferable to dry the PAsp crosslinked material by a reduced-pressure heating drying method, in which it is heated at a temperature of 60°C to 200°C under reduced pressure for 1 to 24 hours, and then grind it into particles using a known grinding device. By performing a cutting process as a pretreatment step, or by performing a cutting process and a drying / grinding process, water-soluble components contained in the PAsp crosslinked material can be effectively removed in the washing process S2.

[0092] Furthermore, in this embodiment, if necessary, the particulate PAsp crosslinked material after the drying and grinding process may be classified, and the washing process S2 may be performed on PAsp crosslinked material within a specific particle size range. This allows for more effective removal of water-soluble components contained in the PAsp crosslinked material during the washing process S2. As a method for classifying the PAsp crosslinked material, known methods such as using a sieve can be used. The particle size range of the classified PAsp crosslinked material can be, for example, 50 μm to 1000 μm, and preferably 100 μm to 750 μm.

[0093] In the cleaning step S2, a mixed solution of water and alcohol or water can be used as the cleaning solution, and it is preferable to use water. In the washing step S2, if a mixed solution of water and alcohol is used as the washing solution, swelling of the PAsp crosslinked material during washing can be suppressed. Therefore, it becomes easier to remove the washing solution from the washed and swollen PAsp crosslinked material. Consequently, the dehydration step S3, described later, which dehydrates the washed and swollen PAsp crosslinked material, can be performed efficiently. Furthermore, if the drying step S4, described later, is performed on the washed PAsp crosslinked material without performing the dehydration step S3, the drying step S4 can be performed efficiently.

[0094] Examples of alcohols that can be included in a water-alcohol mixture include methanol, ethanol, isopropanol, and butanol. The mixing ratio of water to alcohol in a water-alcohol mixture can be determined according to the type of alcohol, etc., and is not particularly limited.

[0095] In the cleaning process S2, when water is used as the cleaning solution, the solubility of water-soluble components in the cleaning solution is higher compared to when a mixed solution of water and alcohol is used. Therefore, for example, when water is used as the cleaning solution, the cleaning effect is higher compared to when a mixed solution of water and alcohol is used, and water-soluble components contained in the PAsp crosslinked material can be removed more effectively.

[0096] The washing step S2 preferably includes a step of immersing the PAsp crosslinked material in a mixed solution of water and alcohol, or in water, in an amount of 10 to 100 times the mass of the PAsp crosslinked material, and stirring for 0.5 hours to 1 hour. If the amount of mixed solution or water used in the washing step S2 is 10 times or more the mass of the PAsp crosslinked material, water-soluble components contained in the PAsp crosslinked material can be effectively removed. More preferably, the amount of mixed solution or water used in the washing step S2 is 20 times or more the mass of the PAsp crosslinked material, and even more preferably 30 times or more. Furthermore, if the amount of mixed solution or water used in the washing step S2 is 100 times or less the mass of the PAsp crosslinked material, it is preferable because less mixed solution or water is needed for washing. More preferably, the amount of mixed solution or water used in the washing step S2 is 80 times or less the mass of the PAsp crosslinked material, and even more preferably 50 times or less.

[0097] Furthermore, if the stirring time when the PAsp crosslinked material is immersed in a mixed solution or water in an amount of 10 to 100 times its mass is 0.5 hours or longer, water-soluble components contained in the PAsp crosslinked material can be removed more effectively. A stirring time of 0.6 hours or longer is more preferable, and 0.7 hours or longer is even more preferable. Also, if the stirring time when the PAsp crosslinked material is immersed in a mixed solution or water in an amount of 10 to 100 times its mass is 1 hour or less, the washing process S2 can be performed efficiently, resulting in excellent productivity. A stirring time of 0.9 hours or less is more preferable.

[0098] The better the water retention of the PAsp crosslinked material, the less likely it is that water-soluble components will be released from the PAsp crosslinked material when it is immersed in a mixed solution or water and stirred. This is because the water-soluble components, while dissolved in water, are firmly held together with the water by the crosslinked structure of the PAsp crosslinked material.

[0099] PAsp crosslinked materials with particularly good water retention include, for example, a PAsp crosslinked material comprising a constituent unit (a) represented by formula (3), a constituent unit (b) represented by formula (4), and a constituent unit (c) represented by formula (6), wherein L in formula (6) is a linear alkylene group having 3 carbon atoms.

[0100] If the PAsp crosslinked material has particularly good water retention properties, and the washing step S2 for washing the crosslinked material involves immersing the PAsp crosslinked material in a mixed solution of water and alcohol in an amount of 10 to 100 times the mass of the PAsp crosslinked material, or in water, and stirring for 0.5 hours to 1 hour, it is preferable to perform the dehydration step S3 described later. This is because, by performing the dehydration step S3, even if the PAsp crosslinked material has particularly good water retention properties, water-soluble components contained in the PAsp crosslinked material can be effectively removed along with the mixed solution or water.

[0101] Furthermore, if the PAsp crosslinked material has particularly good water retention properties, it is also preferable to perform a washing step S2 in which the PAsp crosslinked material is immersed in a mixed solution or water with a mass of more than 100 times but less than or equal to 600 times the mass of the PAsp crosslinked material and stirred for more than 1 hour but less than or equal to 16 hours.

[0102] If the amount of mixed solution or water used in the washing step S2 is more than 100 times the mass of the PAsp crosslinked material, water-soluble components contained in the PAsp crosslinked material with good water retention can be effectively removed without performing the dehydration step S3 described later. In this case, it is more preferable that the amount of mixed solution or water used is 200 times or more the mass of the PAsp crosslinked material, and even more preferable that it is 300 times or more. Furthermore, if the amount of mixed solution or water used in the washing step S2 is 600 times or less the mass of the PAsp crosslinked material, it is preferable that the increase in the amount of mixed solution or water used for washing is suppressed, and less energy is required when stirring. It is more preferable that the amount of mixed solution or water used in the washing step S2 is 500 times or less the mass of the PAsp crosslinked material, and even more preferable that it is 400 times or less.

[0103] Furthermore, if the stirring time when the PAsp crosslinked material is immersed in a mixed solution or water with a mass of more than 100 times but not exceeding 600 times the mass of the PAsp crosslinked material is more than 1 hour, water-soluble components contained in the PAsp crosslinked material, which has good water retention, can be effectively removed without performing the dehydration step S3 described later. The stirring time is more preferably 6 hours or more, and even more preferably 10 hours or more. Also, if the stirring time when the PAsp crosslinked material is immersed in a mixed solution or water with a mass of 600 times or less the mass of the PAsp crosslinked material is 16 hours or less, the decrease in production efficiency due to performing the washing step S2 can be suppressed. The stirring time is more preferably 13 hours or less, and even more preferably 12 hours or less.

[0104] In the washing step S2, known methods can be used to agitate the mixed solution or water in which the PAsp crosslinked material is immersed, such as using a stirring device with stirring blades, and the method can be appropriately determined depending on the amount of PAsp crosslinked material to be washed, the amount of mixed solution or water used, etc.

[0105] In the washing step S2, it is preferable to immerse the PAsp crosslinked material in the mixed solution or water and stir it, then perform a separation step to separate the mixed solution or water from the washed and swollen PAsp crosslinked material, for example, by filtration. The separation step is performed as needed, and may not be performed if, for example, the amount of mixed solution or water used in the washing step S2 is small.

[0106] (Dehydration process S3) In the manufacturing method of this embodiment, it is preferable that the washing step S2 includes a dehydration step S3 for dehydrating the PAsp crosslinked body that has been washed and swollen. In the dewatering step S3, methods for dewatering the washed PAsp crosslinked material include using centrifugal force or using a press.

[0107] Among these methods, it is preferable to use a method that uses centrifugal force to dehydrate the washed PAsp crosslinked material. This is because when the washed PAsp crosslinked material is dehydrated using centrifugal force, the water-soluble components contained in the washed and swollen PAsp crosslinked material are discharged from the PAsp crosslinked material along with the mixed solution or water by the centrifugal force, and are effectively removed from the PAsp crosslinked material.

[0108] One method for dewatering washed PAsp crosslinked material using centrifugal force is to place the washed PAsp crosslinked material in a bag having multiple pores smaller than the particle size of the PAsp crosslinked material, and then dewater it using a known high-speed centrifugal dehydrator.

[0109] (Drying process S4) In the manufacturing method of this embodiment, it is preferable that the washing step S2 includes a drying step S4 for drying the washed PAsp crosslinked material. By performing the drying step S4, the water used in the crosslinking step S1 and / or the mixed solution or water used in the washing step S2 can be removed. The drying step S4 may be performed on a PAsp crosslinked material that has undergone a dehydration step S3 after the washing step S2, or the drying step S4 may be performed on a washed PAsp crosslinked material without performing a dehydration step S3 after the washing step S2.

[0110] In drying step S4, known methods such as heat drying, freeze-drying, reduced pressure (vacuum) drying, and reduced pressure heat drying can be used to dry the washed PAsp crosslinked material. Since the washed PAsp crosslinked material can be dried efficiently, it is preferable to use the reduced pressure heat drying method.

[0111] When drying a washed PAsp crosslinked material using a reduced-pressure heating drying method, for example, a method of heating under reduced pressure at a temperature of 60°C to 200°C can be used. When drying a washed PAsp crosslinked material using a reduced-pressure heating drying method, it is more preferable to heat at a temperature of 60°C to 100°C. The heating time when drying a washed PAsp crosslinked material using a reduced-pressure heating drying method is appropriately determined according to the amount of mixed solution or water contained in the PAsp crosslinked material.

[0112] In this embodiment, after the drying step S4, it is preferable to pulverize the PAsp crosslinked material, which has become a lump after drying, to obtain granular material. The dried PAsp crosslinked material is preferably pulverized so that the particle size classified by sieving is 50 μm or more and 1000 μm or less, more preferably so that the particle size is 100 μm or more and 750 μm or less, and even more preferably so that the particle size is 150 μm or more and 710 μm or less. The dried PAsp crosslinked material can be pulverized using a known pulverizing apparatus.

[0113] Furthermore, in this embodiment, if necessary, the pulverized particulate PAsp crosslinked material may be classified after the drying step S4. Classifying the pulverized particulate PAsp crosslinked material is preferable because, for example, when the silica particle mixing step S5 is performed after the drying step S4, it becomes easier to obtain polyaspartic acid crosslinked material particles with good uniformity in the amount of silica particles arranged on the surface of the PAsp crosslinked material.

[0114] After the drying step S4, known methods such as using a sieve can be used to classify the pulverized particulate PAsp crosslinked material. The particle size range of the classified PAsp crosslinked material can be, for example, 50 μm to 1000 μm, preferably 100 μm to 750 μm, and more preferably pulverized to a particle size of 150 μm to 710 μm.

[0115] (Silica particle mixing process S5) In the silica particle mixing step S5, the washed PAsp crosslinked material and silica particles are mixed to produce polyaspartic acid crosslinked material particles in which multiple silica particles are arranged on the surface of the PAsp crosslinked material.

[0116] In the silica particle mixing step S5, known methods can be used to mix the washed PAsp crosslinked material with the silica particles, such as mixing in a batch kettle or continuous mixing.

[0117] As silica particles to be mixed with the PAsp crosslinked material, it is preferable to use amorphous silica such as hydrophilic fumed silica particles, as this yields polyaspartic acid crosslinked particles with good water absorption properties. The silica particles contained in the polyaspartic acid crosslinked particles have a specific surface area of, for example, 160 m². 2 / g or more 250m 2 It is possible to use those that are less than / g, 170m 2 / g or more 230m 2 It is preferable to use one that is less than or equal to / g, 175m 2 / g or more 225m2 It is more preferable to use a product that is less than or equal to / g.

[0118] In the silica particle mixing step S5, it is preferable to mix 0.1 to 5 parts by mass of silica particles with 100 parts by mass of the washed and dried PAsp crosslinked body. This is because it is possible to obtain polyaspartic acid crosslinked body particles with better water absorption under pressure, containing 0.1 to 5 parts by mass of silica particles with 100 parts by mass of PAsp crosslinked body. The amount of silica particles mixed is more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more. Furthermore, the amount of silica particles mixed is more preferably 3% by mass or less, and even more preferably 2% by mass or less.

[0119] (Heat treatment step S6) In the heat treatment step S6, the polyaspartic acid crosslinked material particles, which have multiple silica particles arranged on the surface of the PAsp crosslinked material produced in the silica particle mixing step S5, are heated at a temperature of 100°C to 200°C for 1 to 60 minutes. By performing the heat treatment step S6, the multiple silica particles arranged on the surface of the PAsp crosslinked material can be more firmly fixed to the surface of the PAsp crosslinked material. The heat treatment step S6 is a step that is performed as needed when the silica particle mixing step S5 has been performed, and is not required.

[0120] Furthermore, in this embodiment, if necessary, the obtained polyaspartic acid crosslinked particles may be classified after the silica particle mixing step S5 or after the heat treatment step S6. As a method for classifying the polyaspartic acid crosslinked particles, known methods such as using a sieve can be used.

[0121] The size (average particle diameter) of the polyaspartic acid crosslinked particles after classification is preferably 1 μm to 5000 μm, more preferably 10 μm to 2000 μm, even more preferably 50 μm to 1500 μm, particularly preferably 100 μm to 1000 μm, and even more preferably 100 μm to 750 μm. When the average particle diameter of the polyaspartic acid crosslinked particles is 1 μm to 5000 μm, it can be preferably used as a material for water absorbents. By following the above steps, the polyaspartic acid crosslinked particles of this embodiment can be produced.

[0122] In this embodiment, as a preferred example of a method for producing polyaspartic acid crosslinked particles, the case in which all steps from the crosslinking step S1 to the heat treatment step S6 shown in Figure 1 are performed is described. However, the dehydration step S3 and the drying step S4 are steps that are performed as needed and may not be performed. In addition, the silica particle mixing step S5 and the heat treatment step S6 are steps that are performed when producing polyaspartic acid crosslinked particles in which multiple silica particles are arranged on the surface of the PAsp crosslinked material, and may not be performed.

[0123] [Water absorbent] The water-absorbing agent of this embodiment contains the polyaspartic acid crosslinked particles of this embodiment. The polyaspartic acid crosslinked particles contained in the water-absorbing agent of this embodiment may be of one type or two or more types.

[0124] The water-absorbing agent of this embodiment may consist solely of the polyaspartic acid crosslinked particles of this embodiment, or it may contain other components along with the polyaspartic acid crosslinked particles of this embodiment. Examples of other components include absorbent resins other than the polyaspartic acid crosslinked particles of this embodiment, known additives, and so on.

[0125] Examples of absorbent resins other than the polyaspartic acid crosslinked particles in this embodiment include other bio-based absorbent resins that are not polyaspartic acid crosslinked, such as polyglutamic acid and polysaccharide-based absorbent resins.

[0126] Examples of additives include gel stabilizers, metal chelating agents, and fluidity enhancers (lubricants). Among these, it is preferable to use a fluidity enhancer (lubricant) as an additive. It is preferable to use inorganic particles as the fluidity enhancer. Examples of inorganic particles include silica particles such as amorphous silica, talc, and mica. The additive components may be located inside the polyaspartate crosslinked particles, on the surface of the polyaspartate crosslinked particles, or both.

[0127] The polyaspartic acid crosslinked particles of this embodiment have excellent water retention and water absorption under pressure, and are therefore suitable for use as a material for water absorbents. Water absorbents containing the polyaspartic acid crosslinked particles of this embodiment can be used in various products where water absorption, moisture absorption, etc., are required.

[0128] Specifically, the absorbent material containing the polyaspartic acid crosslinked particles of this embodiment is used in medical and hygiene products such as sanitary napkins, diapers, breast pads, incontinence pads, portable toilets, wet wipes, medical underpads, medical blood absorbents, and wound dressings; cleaning products such as disposable cloths; pet supplies such as pet sheets; daily necessities and clothing such as disposable hand warmers, sweat-absorbing fibers, and deodorizing and dehumidifying sheets; food freshness preservatives, dehydrators in the food industry, and other fields. It can be used in food-related products such as absorbent sheets and other food packaging materials, and transport materials such as water-absorbing sheets for transporting fresh vegetables; building-related products such as condensation-preventing building materials and waterproofing agents for concrete; gasoline dehydrators, gasoline water removers, oil dehydrators, or oil water removers; and agricultural-related products such as water-retaining materials, soil conditioners, floral foam (insulation material for cut flowers), seedling beds, hydroponic vegetation sheets, seed tapes, fluid sowing media, condensation-preventing agricultural sheets, and irrigation solutions.

[0129] Although specific embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications, alterations, and combinations of each configuration, element, and feature can be adopted without departing from the spirit of the present invention. Unless otherwise specified, the terms "include" and "possess" do not exclude the existence of elements other than those referred to as their objects, and these terms are often used interchangeably. The contents of each document referenced herein are incorporated herein by reference as constituting a part of this specification. [Examples]

[0130] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. "Example 1" The crosslinking step S1, washing step S2, dewatering step S3, drying step S4, silica particle mixing step S5, and heat treatment step S6 shown below were carried out in this order to produce the polyaspartic acid crosslinked particles of Example 1.

[0131] (Crosslinking step S1) 160 parts of aspartic acid and 83 parts of 85% by weight phosphoric acid were mixed in a mortar and pestle, transferred to a tray, and reacted at a temperature of 190°C and a pressure of 1.3 kPa for 6 hours. The reaction product obtained was pulverized and washed with distilled water until the filtrate was neutral. After washing, the reaction product was placed in a dryer and vacuum dried at a temperature of 80°C. This yielded 115 parts of polysuccinimide with a weight-average molecular weight of 80,000.

[0132] 8.47 parts of L-lysine hydrochloride, as the crosslinking agent compound (A), were dissolved in 195 parts of distilled water to obtain an L-lysine hydrochloride solution. Then, 100 parts of polysuccinimide prepared by the method described above were mixed with the L-lysine hydrochloride solution, and 82.6 parts of 48% NaOH aqueous solution were added dropwise at room temperature while stirring to adjust the pH of the reaction solution to 11-11.5. After the addition of the NaOH aqueous solution was completed, stirring of the reaction solution was continued at room temperature for another 15 hours. This yielded a reaction solution (solid content 40%) containing the reactant (P1), sodium lysine-added polyaspartate.

[0133] Next, 0.27 parts of ethylene glycol diglycidyl ether (Denacol® EX-810, Nagase ChemteX Corporation), a polyfunctional epoxy compound (B), was added to a reaction solution (40% solid content) containing 25.0 parts of sodium lysine-added polyaspartate, which is the reactant (P1). The mixture was reacted at a temperature of 60°C for 110 minutes to produce the PAsp crosslinked body of Example 1, which is a solid gel.

[0134] (Cleaning process S2) "Pre-treatment process" The PAsp crosslinked material, which is a block-like gel, was cut into string-like strands using a noodle press (cutting process). The string-like PAsp crosslinked material obtained by cutting was then placed in a dryer and vacuum-dried at 60°C for 16 hours. Subsequently, the dried PAsp crosslinked material was crushed into particles using a crush mill (manufactured by Iwatani Co., Ltd.) (drying and crushing process). The obtained particulate PAsp crosslinked material was classified using a stainless steel sieve (JIS Z-8801). This yielded PAsp crosslinked material with particle sizes ranging from 150 μm to 710 μm.

[0135] Next, the PAsp crosslinked materials with particle sizes of 150 μm to 710 μm that had undergone the pretreatment process were immersed in water in a washing container containing 10 times the mass of the PAsp crosslinked materials, and the PAsp crosslinked materials were washed by stirring with a magnetic stirrer for 1 hour. Subsequently, a separation process was performed to separate the washing solution (water) from the washed PAsp crosslinked material by filtration.

[0136] (Dehydration process S3) Next, the washed and swollen PAsp crosslinked material was packed into tea bags (manufactured by LUCKY BEE) and dehydrated using centrifugal force for 10 minutes with a high-speed centrifugal dehydrator (manufactured by Hismart).

[0137] (Drying process S4) The dehydrated PAsp crosslinked material was removed from the tea bag and dried using a vacuum heating drying method. Specifically, it was placed in a vacuum dryer and vacuum dried at a temperature of 60°C for 16 hours. Next, the PAsp cross-linked material, which had become a lump after drying, was crushed using a crushing device (Crush Millser; manufactured by Iwatani Corporation) to obtain granular material. The resulting granular PAsp cross-linked material was classified using a stainless steel sieve (JIS Z-8801). This yielded washed PAsp cross-linked material with particle sizes ranging from 150 μm to 710 μm.

[0138] (Silica particle mixing process S5) For 100 parts by mass of washed PAsp crosslinked material, a specific surface area of ​​200 m² is obtained. 2 0.5 parts by mass of hydrophilic fumed silica particles (AEROSIL200, manufactured by Nippon Aerosil Co., Ltd.) were mixed by stirring with a magnetic stirrer at room temperature for 5 minutes to obtain polyaspartic acid crosslinked particles in which multiple silica particles were arranged on the surface of the PAsp crosslinked material.

[0139] (Heat treatment step S6) Polyaspartic acid crosslinked particles, in which multiple silica particles are arranged on the surface of the PAsp crosslinked body, produced in silica particle mixing step S5, were heated at a temperature of 140°C for 20 minutes. By following the above steps, the polyaspartic acid crosslinked particles of Example 1 were obtained.

[0140] "Examples 2 to 5" In the washing step S2, the mass of the water in which the PAsp crosslinked material was immersed was set to a multiple of the mass of the PAsp crosslinked material as shown in Table 1. Except for this, the polyaspartic acid crosslinked material particles of Examples 2 to 5 were obtained in the same manner as in Example 1.

[0141] "Example 6" Except for the fact that the stirring time of the water in which the PAsp crosslinked material was immersed in the washing step S2 was set to 16 hours, and the drying step S4 was performed on the washed and swollen PAsp crosslinked material without performing the dewatering step S3, the polyaspartic acid crosslinked material particles of Example 6 were obtained in the same manner as in Example 5.

[0142] Example 7 The process was the same as in Example 1, except that in the washing step S2, the mass of water in which the PAsp crosslinked material was immersed was set to a multiple of the mass of the PAsp crosslinked material as shown in Table 1, and the silica particle mixing step S5 and the heat treatment step S6 were omitted. The PAsp crosslinked material obtained by washing, dewatering, and drying was then used as the polyaspartic acid crosslinked material particles of Example 7.

[0143] Example 8 The same process as in Example 3 was followed, except that the silica particle mixing step S5 and the heat treatment step S6 were omitted. The PAsp crosslinked material obtained by washing, dewatering, and drying was then used as the polyaspartic acid crosslinked particle of Example 8.

[0144] "Example 9" The same process as in Example 4 was followed, except that the silica particle mixing step S5 and the heat treatment step S6 were omitted. The PAsp crosslinked material obtained by washing, dewatering, and drying was then used as the polyaspartic acid crosslinked particle of Example 9.

[0145] "Example 10" The same process as in Example 6 was followed, except that the silica particle mixing step S5 and the heat treatment step S6 were omitted. The PAsp crosslinked material obtained by washing and drying was then used as the polyaspartic acid crosslinked particle of Example 10.

[0146] "Examples 11-13" Polyaspartic acid crosslinked particles of Examples 11 to 13 were obtained in the same manner as in Example 4, except that in the silica particle mixing step S5, the amount of hydrophilic fumed silica particles shown in Table 1 was mixed with 100 parts by mass of the washed PAsp crosslinked material.

[0147] "Example 14" In the washing step S2, the stirring time of the water in which the PAsp crosslinked material was immersed was set to 0.5 hours, but otherwise the procedure was the same as in Example 9 to obtain the polyaspartic acid crosslinked material particles of Example 14.

[0148] "Comparative Example 1" The PAsp crosslinked material of Example 1, which is a bulk gel, was subjected to a cutting process, drying and grinding process, and classification in the same manner as the pretreatment process in the washing process S2 of Example 1, to obtain PAsp crosslinked material with particle sizes from 150 μm to 710 μm. The obtained PAsp crosslinked material was subjected to a silica particle mixing process S5 and a heat treatment process S6 in the same manner as in Example 1, without performing the washing process S2 to drying process S4, to obtain polyaspartic acid crosslinked material particles of Comparative Example 1.

[0149] [Table 1]

[0150] For the polyaspartic acid crosslinked particles of Examples 1 to 14 and Comparative Example 1, the amount of water-soluble components extracted, the content of water-soluble components, water retention, water absorption under pressure, and productivity were measured and evaluated using the method described below. The results are shown in Table 2.

[0151] [Measurement of water retention] The polyaspartic acid cross-linked particles of Examples 1 to 14 and Comparative Example 1 were each subjected to water absorption tests in accordance with JIS K-7223. Specifically, samples were taken from the polyaspartic acid cross-linked particles of Examples 1 to 14 and Comparative Example 1, and their masses were measured. The mass of the tea bag (manufactured by LUCKY BEE) used for the measurement was also measured.

[0152] The samples whose mass was measured were placed in tea bags (manufactured by LUCKY BEE) whose mass was also measured, and immersed in physiological saline to swell. Then, the tea bags containing the swollen samples were dehydrated twice using a high-speed centrifugal dehydrator (product name Dry Cyclone; manufactured by Hismart) at a temperature of 25°C, a centrifugal force of 1100G, and for 5 minutes. After dehydration, the mass of the tea bags containing the samples was measured, and the water retention capacity was calculated using the following formula (I). Water retention [g / g] = {(mass of the tea bag containing the sample after dehydration) - (mass of the tea bag) - (weight of the sample)} / (weight of the sample) ... (I)

[0153] [Measurement of water absorption under pressure] For the polyaspartic acid crosslinked particles of Examples 1 to 14 and Comparative Example 1, a pressurized water absorption test was performed in accordance with the description in Japanese Patent Publication No. 2019-131789 and ERT442.2-02, respectively. "ERT" is an abbreviation for the European standard for measuring superabsorbent polymers (EDANA Recommended Test Method).

[0154] Specifically, a filter paper the same size as the inner diameter of a wire mesh support cylinder was placed inside, and the support cylinder was immersed in physiological saline solution to allow the filter paper to absorb the saline solution. The support cylinder was removed from the physiological saline solution, excess saline solution was absorbed with a cloth such as Kimwipes, and a weight was placed inside the support cylinder. The mass of the combined wire mesh support cylinder, weight, and filter paper was measured and used as the blank mass.

[0155] A glass filter was immersed in saline solution placed in a petri dish. The glass filter was positioned with the rough side facing upwards. A piece of filter paper with the same diameter as the glass filter was placed on top of the glass filter. The weight was removed from the wire mesh support cylinder containing filter paper soaked in physiological saline. Approximately 0.1 g of weighed polyaspartic acid crosslinked particles were evenly distributed on the filter paper inside the wire mesh support cylinder as the sample, and the weight was placed on top of that. The entire assembly of the wire mesh support cylinder, weight, sample, and filter paper was then placed on the filter paper on a glass filter in a petri dish.

[0156] The level of saline solution in the petri dish was confirmed to be higher than the position of the wire mesh in the support cylinder. If the level was lower than the wire mesh, more saline solution was added, and the mixture was left to stand for 1 hour. This allowed the polyaspartic acid cross-linked particles, which were the sample, to absorb the saline solution. After standing for 1 hour, the support cylinder with the wire mesh was removed from the saline solution. After wiping off the saline solution dripping from the wire mesh with a cloth such as a Kimwipe®, the mass of the sample, the filter paper, and the support cylinder with the wire mesh containing the weight was measured and recorded as the mass after water absorption.

[0157] Using the mass after water absorption measured in this manner, the blank mass, and the mass of the sample before absorption of physiological saline (sample mass), the water absorption under pressure [g / g] was calculated using the following formula (II). Water absorption under pressure [g / g] = {(mass after water absorption) - (blank mass) - (sample mass)} / (sample mass) …(II)

[0158] [Measuring Productivity] The productivity of polyaspartate crosslinked particles was evaluated based on the energy used for washing and drying the polyaspartate crosslinked particles and the workability (number of workers) of the washing process, according to the following criteria. In the following criteria, the multiple of the washing container capacity is the ratio of the mass of water in which the PAsp crosslinked particles are immersed to the mass of the PAsp crosslinked particles.

[0159] A: Washing container capacity less than 50 times, 1 worker, drying energy per 1 kg of PAsp crosslinked material less than 113,000 kJ. B: Washing container capacity 50 to 100 times, 1 worker, drying energy per 1 kg of PAsp crosslinked material is over 113,000 kJ to 225,000 kJ. C: Washing container capacity more than 10 to 300 times, 2 or fewer workers, drying energy per 1 kg of PAsp crosslinked material more than 225,000 kJ to 675,000 kJ. D: Washing container capacity more than 300 times, number of workers 2 or less, drying energy per 1 kg of PAsp crosslinked material exceeds 675,000 kJ.

[0160] [Amount of water-soluble components extracted] In the washing step S2, the mass of the PAsp crosslinked material that underwent the pretreatment step (mass before washing) and the mass of the PAsp crosslinked material that was dried in the drying step S4 (mass after washing) were measured, and the amount extracted was calculated using the following formula (III) based on these values. Amount of water-soluble components extracted (mass %) = 1 - [mass after washing / mass before washing] × 100 ... (III)

[0161] [Content of water-soluble components] For the PAsp crosslinked material that underwent the pretreatment step of Example 1, the saturated extract amount (mass%), which is the amount of water-soluble components extracted that does not change even when the amount of water used in the washing step S2 is increased and / or the stirring time is extended, was determined.

[0162] Then, the saturated extraction amount was considered to be the amount of water-soluble components contained in the PAsp crosslinks in the polyaspartic acid crosslinked particles when the washing step S2 was not performed, and the amount of water-soluble components contained in the PAsp crosslinks in the polyaspartic acid crosslinked particles was determined using the following formula (IV). Content of water-soluble components (mass %) = Saturation extraction amount - Amount of water-soluble components extracted …(IV)

[0163] [Table 2]

[0164] As shown in Tables 1 and 2, the polyaspartic acid crosslinked particles of Example 1 were found to have better water retention and water absorption under pressure compared to the polyaspartic acid crosslinked particles of Comparative Example 1, which underwent the silica particle mixing step S5 and heat treatment step S6 in the same manner as in Example 1, but without the washing step S2 to drying step S4. This is presumed to be because the polyaspartic acid crosslinked particles of Example 1 contain less water-soluble components in the PAsp crosslinked material compared to the polyaspartic acid crosslinked particles of Comparative Example 1.

[0165] Furthermore, as shown in Examples 1 to 5, it was confirmed that increasing the mass of water in which the PAsp crosslinked material is immersed in the washing step S2 tends to improve the water retention and water absorption under pressure of the polyaspartic acid crosslinked material particles. This is presumed to be because increasing the mass of water in which the PAsp crosslinked material is immersed increases the amount of water-soluble components discharged from the PAsp crosslinked material, thus decreasing the amount of water-soluble components contained in the PAsp crosslinked material.

[0166] Furthermore, the polyaspartic acid crosslinked particles of Examples 1 to 14 all contained water-soluble components in the PAsp crosslinked material at a content of 22% by mass or less. Furthermore, in Example 7, the polyaspartic acid crosslinked particles were washed by immersing the PAsp crosslinked particles in water 300 times their mass for 1 hour. Therefore, the amount of water-soluble components extracted (mass%) can be considered to be the saturated extraction amount (mass%) based on the results of the water-soluble component extraction amounts in Examples 1 to 5, 8, and 9, and it is presumed that no water-soluble components are contained.

[0167] Furthermore, in Examples 3, 4, and 6, where multiple silica particles are arranged on the surface of the PAsp crosslinked body, the amount of water used in the washing step S2 was the same, and it was confirmed that the absorption under pressure was better compared to Examples 8, 9, and 10, where multiple silica particles are not arranged on the surface of the PAsp crosslinked body.

[0168] Furthermore, in Examples 4, 11 to 13, where the amount of water used in the washing process S2 was the same and multiple silica particles were arranged on the surface of the PAsp crosslinked body, Example 11, in which the amount of silica particles added was 1 part by mass per 100 parts by mass of the PAsp crosslinked body, showed the best absorption under pressure.

[0169] Furthermore, as shown in Examples 1 to 14, it was confirmed that productivity was better when the amount of water used in the washing step S2 was small. In particular, in Examples 1 to 4, 8, 9, and 11 to 14, where the PAsp crosslinked material was immersed in a mixed solution or water with a mass of 10 to 100 times the mass of the PAsp crosslinked material and stirred for 0.5 to 1 hour, the productivity was evaluated as "A" or "B", indicating good results. [Industrial applicability]

[0170] The present invention provides polyaspartic acid crosslinked particles with good water retention and water absorption under pressure, a water absorbent containing the polyaspartic acid crosslinked particles, and a method for producing polyaspartic acid crosslinked particles. [Explanation of Symbols]

[0171] S1: Crosslinking process, S2: Washing process, S3: Dehydration process, S4: Drying process, S5: Silica particle mixing process, S6: Heat treatment process.

Claims

1. A method for producing polyaspartic acid crosslinked particles, comprising a washing step of washing a PAsp crosslinked material, which consists of at least one selected from the group consisting of polyaspartic acid crosslinked materials and salts thereof, using a mixed solution of water and alcohol or water.

2. The method for producing polyaspartic acid crosslinked particles according to claim 1, wherein the washing step includes a dehydration step of dehydrating the washed PAsp crosslinked material.

3. The method for producing polyaspartic acid crosslinked particles according to claim 1, wherein the washing step includes immersing the PAsp crosslinked material in the mixed solution or water in an amount of 10 to 100 times the mass of the PAsp crosslinked material and stirring for 0.5 hours to 1 hour.

4. The method for producing polyaspartic acid crosslinked particles according to claim 1, wherein the washing step includes immersing the PAsp crosslinked material in the mixed solution or water in an amount of more than 100 times and up to 600 times the mass of the PAsp crosslinked material, and stirring for more than 1 hour and up to 16 hours.

5. A method for producing polyaspartic acid crosslinked particles according to claim 1, comprising a silica particle mixing step of mixing the washed PAsp crosslinked material with silica particles to arrange a plurality of the silica particles on the surface of the PAsp crosslinked material.

6. The method for producing polyaspartic acid crosslinked particles according to claim 5, wherein in the silica particle mixing step, the silica particles are mixed with 100 parts by mass of the washed and dried PAsp crosslinked material in an amount of 0.1 parts by mass or more and 5 parts by mass or less.

7. A method for producing polyaspartic acid crosslinked particles according to claim 1, comprising a crosslinking step of reacting polysuccinimide, lysine, and a polyfunctional epoxy compound to produce the PAsp crosslinked material.

8. The PAsp crosslinked material comprises at least one selected from the group consisting of polyaspartic acid crosslinked materials and salts thereof, Polyaspartic acid crosslinked particles wherein the content of water-soluble components contained in the PAsp crosslinked material is 22% by mass or less.

9. The polyaspartic acid crosslinked particle according to claim 8, wherein the PAsp crosslinked material comprises a structure in which polyaspartic acid is crosslinked with lysine and a polyfunctional epoxy compound.

10. The polyaspartic acid crosslinked particle according to claim 8, comprising a plurality of silica particles arranged on the surface of the PAsp crosslinked material.

11. A water absorbent containing polyaspartic acid crosslinked particles according to any one of claims 8 to 10.

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